In recent years, liquid crystal display devices are widely used as a display device of smartphones, tablet computers, vehicle-navigation systems, etc. Generally, liquid crystal display devices comprise a liquid crystal panel and a backlight device overlaid on a rear surface of the liquid crystal panel to illuminate the liquid crystal panel. The backlight device comprises a frame (or bezel), a reflective layer, a light guide plate (light guide), an optical sheet (a prism sheet or diffusion sheet), a light source device (light source unit) which apply light incident on the light guide. The light source device includes a wiring substrate such as an FPC and a plurality of light sources (for example light-emitting diodes or LEDs) mounted on the wiring substrate. Such a light source device is held in a predetermined position, for example, by attaching the wiring board to the light guide and the frame with a double-sided tape as an adhesive material.
Conventionally, the width of the frame of a liquid crystal display device is reduced mainly by narrowing the frame on right and left sides thereof. However, in recent years, there is an increasing demand of greatly narrowing the frame on the light source side (light-entering side), which is the widest part of the frame. In order to narrow the frame on the light-entering side, it is necessary to decrease the distance from the light sources (LEDs) to the display area. However, if the distance is shortened, the difference in luminance between a bright portion at where a light source is provided and dark portion where it is not becomes prominent (non-uniformity in luminance). In order to reduce non-uniformity in luminance, it is necessary to reduce the intervals between light sources in the arrangement.
When the distance between a light source and the display area is reduced and further, the intervals between the light sources are reduced, the adhesion area of the double-sided tape which fixes the wiring board to the light guide plate or frame is decreased, making it difficult to assure sufficient adhesion area to maintain the adhesion strength. As a result, the adhesion between the wiring board and light guide may become incomplete, causing such drawbacks that non-uniformity in luminance occurs and the double-sided tape peels off during a drop test, making it difficult to achieve the narrower frame.